I was discussing a unit on logarithms with a friend today and he asked if seeing one of these would help my students’ understanding:

I had to admit that as I’ve never used a slide rule, I didn’t have a clue if it would help them or not. He seemed shocked (he claimed it wasn’t my age that led him to believe I would have used one). He thought it would be part of either my math or math ed coursework. Maple? Yep. Slide Rule? Nope.

So I’m wondering, am I the only math teacher who hasn’t used a slide rule?

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12 Responses to I’ve Never…

I never have. I’d actually love to learn, just to be able to pull one out and calculate something on it. I think this falls in the same category as using an abacus: it’s interesting to study how it works, but certainly not something I’d expect to be part of any math or math ed curriculum.

Most of them cannot ‘abstract’ successfully, yet we expect them to do it all the time. (Depending on which study you read, up to 1/3 of adults do not achieve Piaget’s ‘formal operations’ stage. This has huge implications for secondary school education…)

I learned the basics of how to use a slide rule whenever it was we first did logarithms in school; I guess that was probably the equivalent of grade 9 or so – we learned about Napier’s bones, learned about slide rules (I got my first one then) and learned to use log tables. Calculators were really just coming in then (this was the 70s), some people had them but they weren’t ubiquitous.

I think slide rules can be useful for directly demonstrating that adding logs corresponds to multiplication (at least if it’s explained right).

I’ve also done multiplication and division (and several other computations) using nomograms.

One of the turning points when I was a kid that got me interested in learning math was when my dad gave me his old slide rule. He used it in college (getting an Electrical Engineering degree at Texas Tech) and later as an engineer for NASA working on the Apollo project. He showed me how to do basic arithmetic on it — I was only 8 or 9, so that’s all I really knew anyhow — but through playing around with it, and looking at the logarithmic and square root tick marks, I discovered the basic idea that some things change at an even rate (linearly) and some things change at uneven rates (concave up or concave down). Just the fact that some of the hash marks on the slide rule were evenly spaced and others were bunched up was enough to raise some serious questions about all this math stuff — which I finally put a language to when I took calculus ten years later.

Come to think of it, I believe that experience with the slide rule has formed my entire philosophy about studying and teaching math. My pedagogy today in college sure does look a lot like me playing with a slide rule.